1. Field of the Invention
This invention relates to a method of producing a calcium magnesium acetate (CMA) deicing agent, and further relates to such a method of making two uniform grades of CMA, one having a calcium-to-magnesium mole ratio substantially equal to one and the other having a calcium-to-magnesium mole ratio much greater than one.
2. Description of the Prior Art
U.S. Pat. Nos. 3,624,243 and 3,630,913, granted to Scott, Jr. et al both relate to chemical deicers containing magnesium and aluminum corrosion inhibitors making them especially suited for use on airport runways. Scott teaches the use of solutions containing urea, ethylene glycol, ammonium nitrate and water soluble chromate salts.
U.S. Pat. No. 4,163,079, granted to Beafore, teaches the spraying of belt transportation surfaces with a composition consisting of a water soluble polyhydroxide compound or a monoalkyl ether, and a water soluble organic compound having at least one hydrophilic group.
U.S. Pat. No. 4,245,166, granted to Glanville et al, discloses a composition for reducing the strength of ice consisting of from 5-90 wt.% of a water soluble organic compound selected from the group consisting of alkynols, diols, polyols, ketones, ethers, carboxylic acids and mixtures thereof; and from 1-20 wt.% of a substance containing ammonium ions selected from the group consisting of ammonium acetate, ammonium nitrate, ammonium sulphate, ammonium sulfamate, ammonium formate, ammonium cyanate, ammonium thiocyanate, ammonium carbonate, ammonium pentaborate, and mixtures thereof.
U.S. Pat. No. to Budenholzer et al, No. 2,918,052, teaches the use of metallic sodium and the caustic (NaOH) formed in the reaction of sodium and water, as a deicing agent. The exothermic nature of the sodium and water reaction, together with the freezing point depressant effect exerted by the caustic, results in a dual action deicing agent.
U.S. Pat. No. 4,081,256, granted to Donnelly, discloses a particulate composition which undergoes an endothermic reaction when mixed with water. This composition consists of urea, hydrated sodium acetate, potassium chloride or potassium nitrate, ammonium chloride and quar gum. Donnelly teaches the use of hydrated sodium acetate in applications requiring a reduction in temperature.
A major anticipated field of use for uniform grades of CMA is in the road deicing field. To date, road deicers have mainly consisted of sodium chloride. Although sodium chloride is quite effective as a deicing agent, it presents numerous difficulties and hazards.
Specifically, sodium chloride promotes corrosion of metallic parts and surfaces such as are found on automobiles and other machinery utilizing roads and highways. Furthermore, with the many millions of pounds of sodium chloride which are used on U.S. highways every winter, serious environmental and health questions are raised concerning plant and animal exposure to such large amounts of sodium and chlorine. This is especially relevant when large amounts of the sodium and chloride ions find their way into water ways and ultimately into human drinking water supplies.
Thus, there has been a need in the art for a road deicing agent substitute for sodium chloride which does not present these serious health and environmental questions.
It is anticipated that the major source of calcium carbonate to be used as a raw material in the manufacture of calcium acetates and calcium magnesium acetates is limestone. However, limestone in the United States generally contains small amounts (up to 20 wt.%) of dolomite (CaMg (CO.sub.3).sub.2). Thus, any process which converts raw material limestone to calcium acetate must necessarily, without a prior costly separation step, produce an amount of magnesium acetate.
It has been found however that magnesium acetate also operates as an extremely effective road deicing agent. In fact, magnesium acetate is a more effective deicing agent than calcium acetate. Hence, it is extremely desirable to have a uniform calcium-to-magnesium mole ratio in the final deicing product in order to facilitate its use by the consumer. Unfortunately, because limestone will most likely be used as the commercial source of calcium and magnesium carbonate and because the proportion of dolomite in the limestone varies with the source of the limestone, the magnesium content of any deicer manufactured from limestone will necessarily vary with the source of the limestone used. In general, the magnesium content will always be lower than the calcium content, and in almost no case will the mole ratio of magnesium-to-calcium exceed unity. Because the product compositions will vary, the deicing characteristics will also vary.
Thus, there has been a need in the art for a process of making calcium magnesium acetate deicing agents, from limestone sources having varying amounts of calcium and magnesium carbonates, having uniform calcium-to-magnesium mole ratios.